Manufacturing method of low-temperature high-rate lithium ion battery

Abstract

The invention discloses a manufacturing method of a low-temperature high-rate lithium ion battery. The low-temperature high-rate lithium ion battery is composed of a positive plate, a negative plate, a diaphragm and an electrolyte, the positive plate is composed of a positive current collector and a positive material coated on the positive current collector; the positive electrode material comprises a positive electrode active material, a binder and a conductive agent; the positive current collector is aluminum foil; the positive electrode binder is PVDF with high molecular weight, and the molecular weight is greater than or equal to 110,000; the positive electrode conductive agent is a mixture of three of graphene, a carbon nanotube (CNT) and a conductive agent SP with excellent conductivity; high-rate lithium cobalt oxide is used as the positive electrode material, the rate discharge performance is excellent, and D50 is controlled to be 5-7 microns; and the binder adopts PVDF with the molecular weight of more than or equal to 110,000, the addition amount is small, and the binding effect is good.

Description

Technical Field

[0001] The present application relates to the technical field of lithium battery manufacturing, and specifically to a method for manufacturing a low-temperature and high-rate lithium-ion battery. Background Art

[0002] With the development of science and technology, electronic products are developing more and more widely, making people's lives more convenient. Electronic intelligent products require power sources. Lithium-ion batteries are widely used in various electronic products as power sources to provide energy due to their excellent performance such as high energy density, long cycle life, and low self-consumption. According to the characteristics of the product and the environment in which it is used, the requirements for lithium-ion batteries are different. Lithium-ion batteries can be classified into low-temperature batteries, conventional batteries, and high-temperature batteries according to the ambient temperature of use. Some products that need to be used in low-temperature environments, such as cold chain transportation, heating clothing, heating shoes, military navigation, electronic cigarettes, and drones, have low discharge efficiency at low temperatures for conventional batteries and high-temperature batteries, and may even fail to discharge electricity, affecting product functions. Therefore, low-temperature lithium-ion batteries are needed. Current low-temperature batteries have some problems, such as low discharge efficiency at low temperatures, and flatulence is prone to occur at room temperature and high temperatures above 45°C. Some products will experience high temperatures during transportation and use, resulting in product failure and malfunction. Summary of the invention

[0003] The purpose of the present application is to provide a method for manufacturing a low-temperature and high-rate lithium-ion battery to solve the problems raised in the above-mentioned background technology.

[0004] The present application provides a method for manufacturing a low-temperature, high-rate lithium-ion battery, which adopts the following technical solution:

[0005] A method for manufacturing a low-temperature, high-rate lithium-ion battery, comprising:

[0006] The low-temperature high-rate lithium-ion battery is composed of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte;

[0007] The positive electrode sheet is composed of a positive electrode current collector and a positive electrode material coated on the positive electrode current collector;

[0008] The positive electrode material includes a positive electrode active material, a binder, and a conductive agent;

[0009] The positive electrode current collector is aluminum foil;

[0010] The positive electrode binder is high molecular weight PVDF, with a molecular weight of ≥ 1.1 million;

[0011] The positive electrode conductive agent is a mixture of graphene, carbon nanotubes (CNT) and conductive agent SP with excellent conductive properties.

[0012] Optionally, the mass ratio of the positive electrode active material, the positive electrode binder and the conductive agent is: 95-96%: 1.0-1.5%: 3%-3.5%.

[0013] Optionally, the negative electrode sheet is composed of a negative electrode active material, CMC, a negative electrode binder, a conductive agent, and copper foil, and the mass ratio of the active material, CMC, negative electrode binder, and conductive agent is 94-95%: 1.2-1.5%: 1.5-2.0%: 2-2.5%.

[0014] Optionally, the negative electrode sheet is composed of a negative electrode active material, CMC, a negative electrode binder, a conductive agent, and copper foil, and the mass ratio of the active material, CMC, negative electrode binder, and conductive agent is 94-95%: 1.2-1.5%: 1.5-2.0%: 2-2.5%.

[0015] Optionally, the negative electrode active material is high-rate artificial graphite, and D50 is controlled to be 7±2 um.

[0016] Optionally, the negative electrode binder is a mixture of SBR (styrene-butadiene rubber latex) and PAA (polyacrylate) in a ratio of 5:5.

[0017] Optionally, the negative electrode conductive agent is one or more of carbon nanotubes (CNT), conductive carbon fibers (VGCF), conductive carbon black, conductive graphite, acetylene black, and graphene composite conductive agents.

[0018] Optionally, the diaphragm is a single-sided ceramic single-sided adhesive diaphragm or a single-sided ceramic double-sided adhesive diaphragm.

[0019] Optionally, the electrolyte is a low-temperature and high-rate electrolyte, the solvent contains 18% to 23% ethylene carbonate, 8% to 12% propylene carbonate, 20% to 25% ethyl methyl carbonate, 40% to 45% ethyl propionate (abbreviated as EP), etc., the additives contain 1% to 2% VC, 1% to 2% PS, 0.5 to 1% DTD, 1-2% ODFB, 0.5-1% MMDS, the electrolyte is LiPF6 with a content of 1.2-1.3 mol, and the conductivity is controlled to be ≥10.0ms / cm.

[0020] Optionally, the positive electrode active material, positive electrode binder, conductive agent and solvent are mixed uniformly in a mass ratio of 95.0-96.0%: 1-1.5%: 3%-3.5%: 25-35% to obtain a positive electrode slurry, and the positive electrode slurry is uniformly coated on the surface of an aluminum foil, dried, and the surface density is controlled to be ≤24 mg / cm2. The positive electrode is rolled and the compaction is controlled to be 3.4-3.8 g / cm3 to obtain a positive electrode sheet.

[0021] Optionally, the negative electrode active material, CMC, conductive agent, negative electrode binder and solvent are mixed uniformly in a mass ratio of 94-95%: 1.2-1.5%: 2-2.5%: 1.5-2.0%: 110-120% to obtain a negative electrode slurry, and the negative electrode slurry is uniformly coated on the surface of the copper foil, dried, and the surface density is controlled to be ≤12mg / cm2 (design CB value ≥1.12), and rolled, and the compaction is controlled to be 1.45-1.55g / cm3 to obtain a negative electrode sheet.

[0022] In summary, the present application includes at least one of the following beneficial technical effects:

[0023] Conductive agents are mixed with SP, CNT and graphene to achieve point, line and surface conductivity, improving the conductivity of the positive electrode; at the same time, high-rate negative electrode materials D50 are selected to be controlled at 7-9um; the binder is a 5:5 mixture of SBR (styrene-butadiene rubber latex) + PAA (polyacrylate) with excellent low temperature performance; the low-temperature conductivity and stability of the electrolyte are improved by adding a variety of additives, and 0.5%-1% MMDS is added to the electrolyte. MMDS can reduce the gas production during the formation of (LiCoO2) / graphite soft-pack batteries and modify the S on the surface of the negative electrode. The EI film makes the SEI film formation at the negative electrode interface more complete, reduces the occurrence of side reactions, reduces the thickness of the positive electrode CEI film and thus reduces the impedance; adding 0.5%-1% DTD as a negative electrode film-forming additive can not only effectively reduce the impedance, but also improve the high-temperature storage performance of the battery; adding 1-2% ODFB improves the low-temperature conductivity and high-temperature stability of the electrolyte, taking into account the high and low temperature performance of the battery, and using a coated separator to bond the positive and negative electrodes together to reduce the ion propagation distance, which not only improves the battery's rate performance, but also reduces the probability of battery deformation. DETAILED DESCRIPTION

[0024] The following is a further detailed description of the application in conjunction with the specification.

[0025] The present invention is described in detail below in conjunction with specific embodiments. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention.

[0026] The following takes the square soft-pack lithium-ion battery model 501447-280mAh as an example.

[0027] Example:

[0028] Preparation of positive electrode:

[0029] The positive electrode active material lithium cobalt oxide, the binder PVDF and the conductive agent are dispersed in N-methylpyrrolidone to obtain a uniform positive electrode slurry; in the positive electrode slurry, the solid component contains 95.7wt% of the positive electrode active material, 1.3wt% of the binder PVDF, 0.8wt% of (multi-walled carbon nanotubes CNT+graphene), and 2.2wt% of the conductive carbon SP; the positive electrode slurry is evenly coated on both sides of the aluminum foil, dried, and compacted by a roller press, with a surface density of 24mg / cm2 and a compaction density of 3.55g / cm3 to obtain a positive electrode sheet.

[0030] Preparation of negative electrode:

[0031] The negative electrode active material graphite, binder SBR, thickener CMC and conductive carbon black are mixed and dispersed in deionized water to obtain a negative electrode slurry; in the negative electrode slurry, the solid components include 94.6wt% graphite, 1.4wt% CMC, 2.5wt% conductive carbon black, and 1.5wt% SBR. The negative electrode slurry is evenly coated on both sides of the copper foil, dried, and compacted by a roller press, with a surface density of 11.2mg / cm2 and a compaction density of 1.5g / cm3 to obtain a negative electrode sheet.

[0032] Preparation of battery cells:

[0033] The positive electrode sheet and the negative electrode sheet prepared above are welded to the pole ears and the separator is wound to obtain a winding core, and then the battery cell is obtained after packaging, baking, liquid injection, formation and capacity division.

[0034] Example 1

[0035] The battery cell was obtained after adding 0.5% ODFB to the electrolyte, injecting, forming and dividing the capacity.

[0036] Example 2

[0037] The battery cell was obtained after adding 1% ODFB to the electrolyte, injecting, forming and dividing the capacity.

[0038] Example 3

[0039] The battery cell is obtained after adding 2% ODFB to the electrolyte, injecting, forming and dividing the capacity.

[0040] 5) Comparative Example 1

[0041] The difference between Comparative Example 1 and Example 2 is that ODFB is not added to the electrolyte, and the other aspects are the same.

[0042] 6) Test method: Take 5 batteries with the same number in each scheme and place them in a 25℃ environment: 1C constant current and constant voltage charging to 4.2V, 0.05C cut-off; 1C discharge to 3.0V and record capacity C1; 1C constant current and constant voltage charging to 4.2V, 0.05C cut-off; 3A discharge to 3.0V and record capacity C2; 1C constant current and constant voltage charging to 4.2V, 0.05C cut-off; leave at -10℃ for 4h, discharge at 3A to 3.0V, record discharge capacity C3. After the test, leave at 25℃ for 4h, charge at 1C constant current and constant voltage to 4.2V, 0.05C cut-off; leave at -40℃ for 4h, discharge at 0.5C to 2.5V, record discharge capacity C4.

[0043] 7) 60℃ high temperature storage for 7 days test method:

[0044] In an environment of 25°C: 1C constant current constant voltage charging to 4.2V, 0.05C cut-off; 1C discharge to 3.0V recording capacity C1; 1C constant current constant voltage charging to 4.2V, 0.05C cut-off;

[0045] The fully charged battery was placed at 60℃ for 7 days, and then placed at 25℃ for 2h to observe whether the battery would swell. The capacity retention and recovery rates were tested. The battery was discharged at 1C to 3.0V, and the discharge capacity was recorded as C2. The battery was charged at 1C constant current and constant voltage to 4.2V, and the battery was cut off at 0.05C. The battery was discharged at 1C to 3.0V, and the capacity was recorded as C3.

[0046] The following table shows the test results of the embodiments and comparative examples:

[0047] Capacity and rate test data at room temperature 25℃:

[0048]

[0049] Table 1.1-10℃ low temperature 3A discharge efficiency

[0050]

[0051]

[0052] Table 1.2-40℃ low temperature 0.5C discharge efficiency

[0053]

[0054] Table 1. 7-day fully charged storage at 360°C

[0055]

[0056]

[0057]

[0058] Table 1.4

[0059] From the data in Table 1.1 to Table 1.4, it can be seen that the room temperature rate performance of the three embodiments and the comparative example batteries are all excellent. The rate performance and low temperature discharge performance of the battery with ODFB added to the electrolyte are improved, and the high temperature storage performance is also improved. With the increase of 1% in the amount of ODFB added to the electrolyte, the high temperature storage performance of the battery is improved, solving the problem of flatulence during high temperature storage of the battery. Through data comparison, it is found that the effect of 1% and 2% ODFB addition is equivalent. This design invention ensures both the low temperature performance and the high temperature storage performance of the battery by optimizing the positive and negative electrode design and the electrolyte design.

[0060] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for manufacturing a low-temperature, high-rate lithium-ion battery, characterized in that: include: The low-temperature high-rate lithium-ion battery is composed of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; The positive electrode sheet is composed of a positive electrode current collector and a positive electrode material coated on the positive electrode current collector; The positive electrode material includes a positive electrode active material, a binder, and a conductive agent; The positive electrode current collector is aluminum foil; The positive electrode binder is high molecular weight PVDF, with a molecular weight of ≥ 1.1 million; The positive electrode conductive agent is a mixture of graphene, carbon nanotube (CNT) and conductive agent SP with excellent conductive properties.

2. The method for manufacturing a low-temperature, high-rate lithium-ion battery according to claim 1, characterized in that: The mass ratio of the positive electrode active material, the positive electrode binder and the conductive agent is: 95-96%: 1.0-1.5%: 3%-3.5%.

3. The method for manufacturing a low-temperature, high-rate lithium-ion battery according to claim 1, characterized in that: The negative electrode sheet is composed of negative electrode active material, CMC, negative electrode binder, conductive agent and copper foil, and the mass ratio of the active material, CMC, negative electrode binder and conductive agent is 94-95%: 1.2-1.5%: 1.5-2.0%: 2-2.5%.

4. The method for manufacturing a low-temperature, high-rate lithium-ion battery according to claim 3, characterized in that: The negative electrode active material is high-rate artificial graphite, and D50 is controlled at 7±2 um.

5. The method for manufacturing a low-temperature, high-rate lithium-ion battery according to claim 3, characterized in that: The negative electrode binder is a mixture of SBR (styrene butadiene rubber latex) and PAA (polyacrylate) in a ratio of 5:

5.

6. The method for manufacturing a low-temperature, high-rate lithium-ion battery according to claim 3, characterized in that: The negative electrode conductive agent is one or more of carbon nanotubes (CNT), conductive carbon fibers (VGCF), conductive carbon black, conductive graphite, acetylene black, and graphene composite conductive agents.

7. The method for manufacturing a low-temperature, high-rate lithium-ion battery according to claim 1, characterized in that: The diaphragm is a single-sided ceramic single-sided adhesive diaphragm or a single-sided ceramic double-sided adhesive diaphragm.

8. The method for manufacturing a low-temperature, high-rate lithium-ion battery according to claim 1, characterized in that: The electrolyte is a low-temperature and high-rate electrolyte, the solvent contains 18% to 23% ethylene carbonate, 8% to 12% propylene carbonate, 20% to 25% ethyl methyl carbonate, 40% to 45% ethyl propionate (abbreviated as EP), etc., the additives contain 1% to 2% VC, 1% to 2% PS, 0.5 to 1% DTD, 1-2% ODFB, 0.5-1% MMDS, the electrolyte is LiPF6 with a content of 1.2-1.3 mol, and the conductivity is controlled to be ≥10.0 ms / cm.

9. The method for manufacturing a low-temperature, high-rate lithium-ion battery according to claim 1, characterized in that: The positive electrode active material, positive electrode binder, conductive agent and solvent are mixed uniformly in a mass ratio of 95.0-96.0%: 1-1.5%: 3%-3.5%: 25-35% to obtain a positive electrode slurry, and the positive electrode slurry is uniformly coated on the surface of an aluminum foil, dried, and the surface density is controlled to be ≤24 mg / cm2, and rolled, and the compaction is controlled to be 3.4-3.8 g / cm3 to obtain a positive electrode sheet.

10. The method for manufacturing a low-temperature, high-rate lithium-ion battery according to claim 1, characterized in that: The negative electrode active material, CMC, conductive agent, negative electrode binder and solvent are mixed uniformly in a mass ratio of 94-95%: 1.2-1.5%: 2-2.5%: 1.5-2.0%: 110-120% to obtain a negative electrode slurry, and the negative electrode slurry is uniformly coated on the surface of the copper foil, dried, and the surface density is controlled to be ≤12mg / cm2 (design CB value ≥1.12), and rolled, and the compaction is controlled to be 1.45-1.55g / cm3 to obtain a negative electrode sheet.

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